This release contains an important bug fix which affects the speed of allocating a shard to a new node. The first phase of shard recovery copies all the segment files from the source node to the target node. During this phase, any index, update, or delete requests are recorded in the transaction log, to be replayed on the target node at the end of recovery. If the shard is very large, this transaction log can accumulate many events which need to be replayed.

Previously, merges of new segments were disabled on the target node during recovery. A large transaction log would result in an explosion of small new segments, severely impacting the speed of recovery. Issue #10463 changes the behaviour to enable merges on the target shard during recovery.

Other notable bug fixes include:

Forcing a refresh if too many deletes fill up the version map (#10312)